This research focuses on children's acquisition of intonation or 'the melody of language.' The proposed work is the first step in a long-term research program designed to describe the relation between intonation and grammatical skills in children with normal and disordered language development. The purpose of the long-range program is to test the hypothesis that intonation is a prosodic correlate of children's emerging grammar. An equally compelling clinical impetus for the research comes from an applied corollary of the theoretical hypothesis, namely, the idea that deficits in intonation may identify children with language disorders at a younger age than deficits in 'core' language skills such as syntax. At present, however, the diagnostic significance of infants' expressive intonation can not be determined, because the normal course of intonation development has not been documented. To address this issue, the present application aims to demonstrate, first, that acoustic analysis procedures recently used to describe intonation development in toddlers from 18 to 24 months can be used successfully with even younger children. Second, the project aims to identify the age or period of linguistic development in which the majority of normally developing children produce one or more adult-like intonation contours. Towards these ends, the project will perceptually and instrumentally analyze the vocalizations of 10 children in each of five cross-sectional age groups: 6-8 months, 9-11 months, 12-14 months, 15-17 months, and 18-20 months. Perceptual analysis of a 30-minute sample of spontaneous speech will be used to determine each child's stage of vocal development. Acoustic analysis will determine whether each infant consistently produces a rising or falling intonation contour. The research hypothesis predicts that 75 percent of the children in the single-word or two- word periods will produce a falling or rising contour, but fewer than 75 percent of infants in the prelinguistic period will do so. The findings of this project will contribute to the long-term research because they will provide an estimate of the earliest age or developmental period in which normal and abnormal patterns of intonation production can be distinguished.